Vibra-tone volume drop

[SonicVI]

I wired up my Vibra-tone build tonight using Markm's layout with the extra JFET stage and trimpot and I still get a significant volume drop.  The effect is working, but the volume is low. I've double checked my component placement and wiring and the only thing I could think of to do was try swapping out Q11 with another 2n5259's in case the one I used had too low of gain or something, but to no avail.  I also tried swapping Q1 and Q4.  Is there anything else I can try?

[SonicVI]

Here are voltages on the transistors:

V+ = 9.22V

Q1:
D- 9.21
S- 4.77
G- 3.22

Q2:
D-5.11
S-2.74
G-1.48

Q3:
D-5.1
S-2.74
G-1.45

Q4:
D-9.21
S-4.78
G-3.47

Q5:
D-1.19
S-1.19
G- oscillating between about .12-.21

Q6:
D-4.5
S-1.19
G-.4

Q7,Q8 & Q9: and swinging widely from low to high

Q10: omitted

Q11:
D-4.53
S-2.12
G-.75



I've done some audio probing and I get the same volume before and after the last JFET gain stage, which makes be believe there's something wrong there.

[SonicVI]

Found a fix.  I did some studying up on JFET gain stages and saw that most of the jfet mini-booster type circuits have a bypass cap from source to ground whereas markm's final gainstage does not.  So I added a 22uF cap across R38 and it brought the level up significantly.    Now I just need to get rid of the beating at high intensity. 

[bluesdevil]

Went through all these problems as well when finally getting mine to work (missed a ground wire from a pot!). I didn't put a bypass cap on the jfet boost stage, I just ripped it out and put a LPB-1 on the output for increased volume. The beating may stop once you put it in a enclosure, but I went the whole 10 yards with shielded wiring on everything and even seperated the LFO ground from the board to the "star point" (output jack ground lug). It helped quite a bit and totally stopped "beating" when enclosed.
     Very nice effect!

[SonicVI]

I do have it in an enclosure already.  The beating stops with the depth at about 50% or less. There's really not  great deal of difference in the sound in the last 50% of rotation anyway, but I'd still like to get it worked out.  I don't know if I want to go through the hassle of shielded wire on everything. Maybe I'll try the in and out wires, but I'm skeptical that that will help. I'd prefer to find another remedy.

[bluesdevil]

I do have it in an enclosure already.  The beating stops with the depth at about 50% or less. There's really not  great deal of difference in the sound in the last 50% of rotation anyway, but I'd still like to get it worked out.  I don't know if I want to go through the hassle of shielded wire on everything. Maybe I'll try the in and out wires, but I'm skeptical that that will help. I'd prefer to find another remedy.

I hear you about not wanting to shield the wires.... not fun. On my build, not one thing got rid of the "beating", but the combination did. Maybe first try  rerouting the LFO and power grounds to the output jack, but you'll have to cut some traces and drill. Maybe you can find the thread I started when I had my problems for some info I got from others. Good luck with whatever you decide to do to get this thing quiet.

[SonicVI]

I socketed the LFO transistors to play around with different transistors and gain and I put a 2N5133 with gain of about 240 in Q9 and the ticking is gone. The effect doesn't seem quite as deep now, so I'm going to keep playing with tranistors and gain to try to find the highest gain I can get without ticking.  Still sounds really nice either way. I also had to add a cap from the output to ground to kill some of the background noise.

[SonicVI]

I do have it in an enclosure already.  The beating stops with the depth at about 50% or less. There's really not  great deal of difference in the sound in the last 50% of rotation anyway, but I'd still like to get it worked out.  I don't know if I want to go through the hassle of shielded wire on everything. Maybe I'll try the in and out wires, but I'm skeptical that that will help. I'd prefer to find another remedy.

I hear you about not wanting to shield the wires.... not fun. On my build, not one thing got rid of the "beating", but the combination did. Maybe first try  rerouting the LFO and power grounds to the output jack, but you'll have to cut some traces and drill. Maybe you can find the thread I started when I had my problems for some info I got from others. Good luck with whatever you decide to do to get this thing quiet.

I'm not sure what you mean by rerout the lfo and power grounds?

[bluesdevil]

Sorry, I can't remember where I made the exact trace cuts, but what I meant was out of desperation I tried disconnecting the ground of the LFO circuit from the ground of the audio path. I star grounded everything at the output jack.... same with the ground coming out of my power adaptor jack (didn't use a battery or R.G.'s PNP transistor circuit either).
   Doing that along with shielded the wiring helped, but didn't completely get rid of the beat. Putting in an enclosure did the trick so maybe it was for nothing in my case anyway.  I'm no engineer, just grasped for straws when I ran into the same problem, but got it to work by luck probably.
   By the way, I could make the noise go away by using two separate pots instead of the dual by fiddling around a bit with it, but as soon as I found the settings I liked (and without the beat), the LFO would freeze up. I wound up saying the hell with it and went back to the dual pot and luckily it worked out for me in the end. Maybe someone else more technically sound can chime in soon as well.

[SonicVI]

Sorry, I can't remember where I made the exact trace cuts, but what I meant was out of desperation I tried disconnecting the ground of the LFO circuit from the ground of the audio path. I star grounded everything at the output jack.... same with the ground coming out of my power adaptor jack (didn't use a battery or R.G.'s PNP transistor circuit either).
   Doing that along with shielded the wiring helped, but didn't completely get rid of the beat. Putting in an enclosure did the trick so maybe it was for nothing in my case anyway.  I'm no engineer, just grasped for straws when I ran into the same problem, but got it to work by luck probably.
   By the way, I could make the noise go away by using two separate pots instead of the dual by fiddling around a bit with it, but as soon as I found the settings I liked (and without the beat), the LFO would freeze up. I wound up saying the hell with it and went back to the dual pot and luckily it worked out for me in the end. Maybe someone else more technically sound can chime in soon as well.

Maybe RG could give an opinion? 
If this is not a problem for everybody and everybody is not shielding every wire then it would seem that there must be some component based variable here that is the cause, and my guess would be it's the transistors since they're the most variable of all the components used.  I'll probably concentrate on that that for a while and see if maybe changing out JFETs will help.